An antenna tuner is connected between a wireless device's radio frequency (RF) front end and antenna to improve power transfer by matching the impedance at the output of the RF front end, which is typically 50 ohms, to the antenna. For any non-50 ohm antenna impedance, the antenna tuner aims to transform the antenna impedance into a 50 ohm impedance at the input of the antenna tuner such that radiated power is maximized.
For this purpose, an antenna tuner is operated in a closed loop manner, using the wireless device's RF detector. This RF detector is configured to detect the impedance loaded at the output of the RF front end. When the characteristics of transmission lines between the RF front end and the antenna tuner are known, desired impedance at the input of the antenna tuner can be analytically calculated based on the impedance readout and the frequency of operation.
This closed loop approach requires precise knowledge of the transmission lines between the RF front end and the antenna tuner. In addition, immediate implementation of carrier aggregation requires multiplication of antenna modules, and accordingly, the number and complexity of transmission lines which connect the antenna modules to the RF front end in order to operate the antenna tuner.
From a product rollout perspective, this analytical approach requires significant interaction between manufacturers of the RF front end, antenna tuner, and transmission lines. Some manufacturers may not be willing to provide an accurate characterization of the transmission lines of the wireless device to be assembled. Transmission line calibration, which is required in order to operate the antenna tuner in a closed loop manner, is disadvantageous in actual practice.